1. Field of the Invention
This invention relates to a copper based alloy having high strength, for use as a material of electrical and electronic parts, which is free from smutting during pretreatment for plating thereof.
2. Prior Art
Conventionally, as copper based alloys for use in the manufacture of electrical and electronic parts, such as terminals, connectors, and lead frames of semiconductor devices, there have been proposed a copper base alloy which consists essentially, by weight % (hereinafter referred to as "%"), of 1.24% nickel (Ni), 1.80% tin (Sn), 0.052% silicon (Si), 0.55% zinc (Zn), 0.0052% calcium (Ca), 0.0245% magnesium (Mg), 0.0058% lead (Pb), and the balance of copper and inevitable impurities, by Japanese Laid-Open Patent Publication (Kokai) No. 1-272733, and a copper base alloy which consists essentially of 0.05-3.0% Ni, 0.01-1.0% Si, 0.001-0.05% P, and the balance of Cu and inevitable impurities, and which may preferably contain 0.001-3.0% one or more of Zn, Sn, As, Cr, Mg, Mn, Sb, Fe, Co, Al, Ti, Zr, Be, Ag, Pg, B and lanthanide elements, as secondary components, by Japanese Laid-Open Patent Publication (Kokai) No. 2-122039 (hereinafter referred to as "the conventional Cu based alloys")
The percentage used throughout the present specification is percent by weight.
The conventional Cu based alloys are generally rolled into a sheet, and the sheet is then subjected to working, such as blanking and bending, to be formed into electrical or electronic parts with a predetermined shape, followed by plating the thus formed electrical or electronic parts, to thereby obtain final products. To plate the thus formed electrical or electronic parts, e.g. to plate the outer surfaces of leads for a semiconductor device with a solder, the leads for the semiconductor device are subjected to a pretreatment consisting of steps of alkaline electrolytic cleaning, water washing, etching, water washing, smut removing, and water washing. Then, the thus pretreated leads are subjected to plating consisting of steps of pre-dipping, solder plating, water washing, neutralization, water washing, water bathing, blowing, and drying.
Electrical and electronic parts are always demanded to be manufactured at lower costs, and to meet the demand, it is required that electrical and electronic parts should be manufactured by more efficient steps. However, electrical and electronic parts formed from the conventional Cu based alloy undergo smutting during the above-mentioned pretreatment for plating, particularly during the etching step. Since the conventional Cu based alloys contain Ni and Si as mentioned above, a chemical compound mainly composed of Ni.sub.2 Si can precipitate on the surface of the Cu based alloy. A Cu based alloy of this kind is usually subjected to pretreatment and then to plating into a final product. During the pretreatment, the chemical compound mainly composed of Ni.sub.2 Si on the surface of the alloy is not washed off the alloy surface but remains thereon in the form of a smut. To remove the smut, a great deal of time period is required, which unfavorably impedes an improvement in the productivity.